Bits and pieces of headcanon
Headcanon
o Yukinami remembers the first time he used landkarte. He and Suzu were playing with a flying kite on a beach and Yuki accidently let go of it. He then accidently transported it back - in shreds. Five year old Yuki immediately began to cry, but he didn’t have much time to do so. That’s because Suzu shouted ‘that was the coolest thing ever! Do it again!’ and so everything was great again. Yuki beamed with pride and joy upon realizing he’s done something so cool. He also noticed that some of the other children on the beach were staring at them, which meant that Suzu was right. But that’s obvious, because Suzu was always right.
o When they were four years old, they used to build a lot of small sandcastles in the sandbox. Once, one of their sandbox friends was very impressed with Suzu’s building skills (he he build a big, solid sandcastle). She ‘proposed’ to Suzu just like she saw her stepfather propose to her mom. In other words, she knelt and shouted: ‘Please be my other half, Suzu! I can’t live without you!’ Suzu, bewildered, tugged Yuki closer (by his hair), hairruffled him and told the girl ‘That’s too bad. Maybe go see doctor? Anyway, you no Yuki.’ Afterwards Yuki made an enormous sandcastle for Suzu - it took him five hours. It was bestest ever. For sure. And in the evening, when mother was kissing them goodnight, Yuki, nodding earnestly, told her about his illumination. In the tone of a person sharing the ultimate secret of universe with somebody, he said ‘Suzu is Suzu.’ Suzu, almost asleep, commented ‘Duh.’
o As a child Yuki always loved fairy tales, especially those about powerful heroes. In all his evening prayers he always thanked God for blessing him by giving him one of those (a real one at that!) as his twin.
o Little Yuki had been afraid of darkness. When Suzunami noticed this, he made a habit of dragging Yukinami to various dark places. Every time Yuki said that he’ll never forgive Suzu if he does it again. Somehow, Suzu didn’t believe him and always did it again. Somehow, Yuki stopped being afraid of darkness when he was seven.
o When they were ten, Suzu once decided they should explore whole forest. He also decided to split out at some point to make their exploration quicker. Yuki had a bad luck and encountered a bear, which could've been fatal for him if he didn't have landkarte. The result wasn't pleasant for him anyway seeing as he ended up with fragments of bear on himself. Suzunami found him still sobbing from fear an hour later and they immediately hugged. It was the only time ever that Yukinami heard Suzu say 'I'm an idiot'. Hearing such a thing confused Yuki so much that he stopped crying and smiled sheepishly.
o Yuki accidently broke so many things by transporting them in his childhood. So no wonder little Yuki was often nervous, thinking'what if I accidently landkarte and break something next minute I don't want to break mom's vases oh God'.
o In the beginning of his time at Academy, Yukinami often wished he had a more common type of zaiphon. Maybe then teachers wouldn’t ask him for a demonstration so often - and he wouldn’t have messed up before the whole class so often. Yuki will always be certain that he wouldn’t have survived Academy if not for Suzu.
o Yukinami has been to an onsen with Ayanami, Hyuuga and Suzu after recovering from his wounds in the end of the manga. He was so happy that Ayanami finally took a day of because Ayanami's always overworked. Yuki was sure that even Ayanami-sama needed to relax from time to time. It was, for sure, one of the best days in Yuki's life so far.